BW Broadcast technical manual
Page 33
Technical data
cation of the PLL locked condition. The front panel control system will also display the locked condition when in
the frequency display screen.
Audio is fed into the modulation input of the exciter from external multiplex input connector CON2 which is a BNC
type or from the internal stereo encoder section by having jumper J1 set to loopthrough. The modulation level can
be adjusted from the back panel by the adjustment of variable resistor VR5 which is in the feedback loop of op-
amp IC18. The output of the op-amp feeds the modulation element, varicap diode VD1, via potential divider R31
and R18.
CON8 provides an interface to the control / LCD board. This ribbon cable interface provides connections for the
alarm signals to the back panel D-type from the microcontroller on the LCD board together with connections for
the modulation, the limiter gain reduction level and a serial interface which provides frequency and status informa-
tion between the PLL microcontroller on the combo board and the main system microcontroller on the LCD board.
3.22 LCD CONTROL BOARD
The LCD control board is the heart of the transmitter. The board contains an eight bit microcontroller, LCD display,
a voltage regulator and a dual op-amp together with a few passive components.
CON1 provides a 10 way interface to the power amplifier board and its sensors. Some of the connections of
CON1 are routed around to the power supply modules. CON2 provides a 16 way interface to the combo board
providing power to the combo board as well as routing signals to the back panel D-type sockets for alarms/RS232
and returning modulation and limiter gain reduction signals to the main microcontroller.
The voltage regulator REG1 and decoupling capacitors C1 and C2 takes the 18 volt auxillary supply from CON1
and regulate it down to 5 volts for the microcontroller and LCD circuitry. The microcontroller is a 40 pin 8 bit type
running at 8 MHz. The microcontroller has several ports that have various functions and connect to external com-
ponents.
PORTA (6 bits) is primarily used for the analogue voltage inputs. Bit 0 is the limiter gain reduction, Bit 1 the modu-
lation, Bit 2 the AUX volts and Bit 3 the Fwd RF power. Bit 4 is not used and bit 5 of PORTA has a control con-
nection to the LCD display.
PORTB (8 bits) has a few different functions. Bits 7,6 and 3 of the port are the alarm signal outputs and are rout-
ed off via CON2 to the D-type on the back of the combo board. Bit's 5,4 and 2 are connected to the front panel
buttons to allow navigation of the LCD functions. Bits 1 and 0 provide a 2 wire interface to the PLL microcontroller
on the combo board.
PORTC (8 bits) bits 0 and 1 are used to write information to the LCD display. Bit 2 is the pulse width modulator
output (PWM) and connects into unity gain DC amplifier op-amp IC2A. The voltage generated by the PWM is set
by the software in the microcontroller. This PWM level is then fed through potentiometer VR2 and smoothed by
C13 before being buffered by the aforementioned op-amp. PORTC bits 3-5 are not used. Bit’s 6 and 7 of PORTC
are used by the UART inside the microcontroller. These pins are RXD and TXD for the RS232 interface. They are
routed via CON2 to the back panel D-type.
PORTD's 8 bit's are interfaced to the 8 bit data bus of the LCD display. The data byte on PORTD can be latched
into the LCD display by the LCD control bits on PORTC.
PORTE (3 bits) has the remaining A/D inputs. Bit 0 is the PA volts, Bit 1 is the Rev RF power and bit 2 is for the
PA temperature.
The microcontrollers software reads all the analogue voltages, converts and displays them where neccessary and
outputs alarm signals in the event of a transmitter error. There are various passive components associated with
IC1. Each A/D port has input current limiting resistors R1-11 and decoupling capacitors C5-11. X1, C3 and C4
provide the 8 MHz signal for the clock of the microcontroller. R12 and R13 provide pull downs for correct opera-
tion of the internal processor communications channel. C12 provides supply decoupling for the microcontroller
and VR1 sets the contrast of the LCD display.
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